This invention relates generally to brush wear indicators for dynamoelectric machines and more particularly to a brush wear indicator which uses light energy conductors, commonly referred to as fiber optics, in a completed or interrupted light path to signal the existence of a worn brush condition.
Dynamoelectric machines such as direct current motors use carbon brushes to transfer power between an external source of electric power and a rotating commutator associated with the rotor the motor. Since the brushes are in contact with the commutator, they must be periodically replaced after a predetermined amount of wear to assure adequate current conduction and to prevent damage to the commutator. Alternating current machines similarly often employ brushes and slip rings for the transfer of electric power with similar wear problems.
A variety of brush wear indicators are known for signalling the need for brush replacement. Typically, such apparatus includes electrical circuitry whose operation is dependent upon the condition of wear as sensed by movement of a self-winding brush follower spring which applies a biasing force against the rear end of the brush the other end of which is in contact with the commutator or slip ring of a dynamoelectric machine. When the brush is in a new or usable condition, the coil of the spring is in a first position away from the commutator. As the brush wears, the coil eventually reaches a second position near the commutator. This movement is utilized to open or close a set of electrical contacts, which thereby energizes or deenergizes an electrical circuit for signalling the need for brush replacement. Examples of such apparatus include that disclosed in U.S. Pat. No. 4,488,078, entitled, "Brush Wear Detector", issued to Ronald C. Orton on Dec. 11, 1984; U.S. Pat. No. 4,344,009, entitled, "Brush Wear Indicator For A Dynamoelectric Machine Brush", issued to Kenneth R. Reynolds on Aug. 10, 1982; and U.S. Pat. No. 4,348,608, entitled, "Brush Wear Indicator", issued to Richard N. Michael on Sept. 7, 1982.
A second well known type of detector system employs an electrical conductor embedded within the brush. When the brush wears by a predetermined amount, the conductor contacts the commutator (or slip ring) which may serve to complete an electric circuit or, as by wearing through a loop at the end of the conductor, break an existing circuit. In either case, a worn brush condition is indicated. These embedded conductor systems suffer from the two primary deficiencies of having an electrical current carrying member in the current carrying brush and, since the conductor is usually metallic, of a metal to metal contact with the commutator or slip ring.
Accordingly, it is an object of the present invention to provide an improvement in brush wear detectors or indicators.
It is a further object of the invention to detect a worn brush in a dynamoelectric machine using light energy.
It is another object of the invention to provide a brush wear indicator which uses light conductors to keep the electrical conductive members associated with the detection/indicator away from the voltages present in the brush assemblies of the dynamoelectric machine.
And yet a further object of the invention is to provide a fiber optic brush wear detector that is protected from contamination such as dirt and the like.